Geothermal

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Standard Page - 2006-01-17

Geo (earth) thermal (heat) energy means harnessing heat from inside the Earth. Our planet's core is incredibly hot – 5,500° C (9,932° F) by recent estimates – so it's no surprise that even the top three metres of Earth's surface stay a nearly constant 10-16° C (50-60° F) year round. Plus, thanks to various geological processes, much higher temperatures can be found in some places.

Geo (earth) thermal (heat) energy means harnessing heat from inside the Earth. Our planet's core is incredibly hot – 5,500° C (9,932° F) by recent estimates – so it's no surprise that even the top three metres of Earth's surface stay a nearly constant 10-16° C (50-60° F) year round. Plus, thanks to various geological processes, much higher temperatures can be found in some places.

Hellisheiði Geothermal Plant is situated at Hengill, an active volcanic ridge in SW Iceland. The Hellisheiði Power Station is the second largest geothermal power station in the world, and the largest in Iceland. The plant´s purpose is to meet increasing demand for electricity and hot water for space heating in the industrial and domestic sectors. Current production capacity is 213 MWe (December 2010). Estimated production capacity for the completed Hellisheiði Plant is 300 MW electricity and 400 MW thermal energy. Once this capacity is reached, it would rank as the largest geothermal power station in the world, in terms of installed capacity.

Putting that heat to work

When geothermal hot water reservoirs are near the surface, their hot water can be piped directly to where the heat is needed. Geothermal can be used to heat homes, to warm greenhouses and even to melt snow on roads.

In areas without easily accessible geothermal reserves, a ground heat pump can bring warmth to the surface and into buildings. This works nearly anywhere, and can also be used for cooling: Because the temperature underground stays nearly constant year round, the same system that provides heat in the winter can help cool the house in summer.

Electricity generation

Geothermal power plants use wells with a depth of 1.5 km (1 mile) or more to tap into boiling hot geothermal reserves. Some power plants use the steam from these reserves to directly turn turbines. Others pump high-pressure hot water into low-pressure tanks. This causes "flashed steam", which is used to turn a turbine generator. A newer kind of plant uses the hot water from the ground to heat another liquid, like isobutene, which boils at a lower temperature than water. When this liquid vaporizes and expands, it turns the turbine generator.

Advantages of geothermal power

Geothermal power generation causes virtually no pollution or greenhouse gas emissions. It doesn't use a fuel – it's virtually continuously renewable. It's also quiet, and extremely reliable. And geothermal's potential is vastly untapped: it's massively under-utilised, even in many countries with abundant geothermal reserves.